By Jake Donovan

A tripleheader of super welterweight title fights topped by Jermall Charlo's defense versus former champ Austin Trout remains on course for May 21, with Showtime likely to televise. However, the official announcement remains on hold due to an inability to secure a venue, which could ultimately prompt a change in location.

Charlo-Trout tops a show that will also include Jermall's twin brother, Jermell who faces John Jackson with the vacant WBC super welterweight title at stake. The evening's chief support is a rematch between defending WBA titlist Erislandy Lara and Vanes Martirosyan. The originally targeted hosting city was Houston, where the Charlos were born, raised and presently live, and also where Lara currently resides and trains (he and Jermall are trained by Ronnie Shields, whom formerly trained Jermell).

However, BoxingScene.com has learned that Space City appears to now be out of the running due to a lack of available venues. The Houston Astros have a home Major League Baseball Game, while Toyota Center and NRG Arena (formerly Reliant Arena) are also booked for that date.

The irony in the card being on the move is that all three visiting fighters - Trout, Martirosyan and Jackson - warmed up to the notion of having to fight in hostile territory.

Trout and Martirosyan previously insisted upon a neutral location for their respective bouts. Martirosyan - who used to train with Shields in Houston - was vocal in his admittedly giving in to any stipulation placed by Lara's camp, as he was that eager to land the fight.

Now it appears that all six boxers will have to embrace a new city in which to fight. Alternatives have varied, with Barclays Center in Brooklyn, DC Armory in Washington D.C. (relatively close to Trout's current training headquarters at Barry Hunter's Headbangers Gym) and Las Vegas all rumored to be in the mix. Given the three-title status of the show - and presumably the price tag that comes with piecing together said bouts, Las Vegas or any major casino location would appear to be the logical Plan B.

The main event will mark the second attempted title defense for Charlo (23-0, 18KOs), who claimed the IBF belt with a 3rd round knockout of Cornelius Bundrage last September. The unbeaten boxer accomplished the feat live as part of the Premier Boxing Champions (PBC) series on NBC, which also aired his first defense - a 4th round stoppage of overmatched Wilky Campfort last November in Dallas, Texas.

His twin brother Jermell (27-0, 12KOs) enjoyed a home game in his last outing, a 6th round stoppage of Joachim Alcine last Halloween at NRG Arena in Houston. The bout was his first under new trainer Derrick James - who also trains unbeaten welterweight contender Errol Spence Jr. - after having separated from Shields. His previous bout took place in Las Vegas, edging out Martirosyan in a disputed decision win.

Jermell's challenger, Jackson (20-2, 15KOs) also fights for his first major title. The second-generation boxer - who is the son of famed former middleweight titlist Julian Jackson, one of the hardest punchers in boxing history - served alongside his brother on the 2008 Virgin Islands Boxing team in Beijing, but endured rough waters early in his career before reaching the title stage. A Sept. '12 points loss to spoiler Willie Nelson stripped him of his unbeaten record, while he was dealt a humbling knockout defeat by Andy Lee in a June '14 clash where he was up on all three scorecards before getting clipped in the 5th round of their HBO PPV-televised preliminary bout.

Two wins have followed for Jackson, including a 10-round decision over Dennis Laurente, which served on the inaugural installment of PBC on Bounce TV last August. The win was designed to lead to a final eliminator with Jorge Cota, whom easily outpointed Yudel Jhonson on the same card. However, he was advanced to the title picture upon Floyd Mayweather's officially vacating the crown upon his retirement last fall. 

Lara (22-2-2, 13KOs) and Martirosyan (36-2-1, 24KOs) previously fought to a technical draw in their Nov. '12 title eliminator in Las Vegas. Both went on to gain separate title challenges; Lara overcame two knockdowns to force Alfredo Angulo into submission in ten rounds to collect an interim title in their June '13 clash, with his title status upgraded after Mayweather returned to welterweight following a win over Saul 'Canelo' Alvarez in their Sept. '13 unification match.

The rematch with Martirosyan - born in Armenia but raised in California and whom served on the 2004 U.S. Olympic Boxing team in Athens - will mark Lara's fifth overall title defense in a reign that also includes a dominant 12-round win over Trout. The Cuban defector has won three straight following a narrow loss to Alvarez in their July '14 non-title fight. 

Martirosyan aims for a second career title shot. The draw with Lara was followed by a knockout win over Ryan Davis followed by a vacant title fight loss to Demetrius Andrade, both of which took place in separate parts of Texas in 2013. He has since won three of his last four starts, with the aforementioned loss to Jermell Charlo followed up by a hard-fought 10-round win over former 154-pound titlist Ishe Smith last September.

Trout (30-2, 17KOs) has won four straight following back-to-back losses in 2013. His previous title reign began on the road with a 12-round win over Rigoberto Alvarez - Canelo's brother - in Mexico in Jan. '11, making four successful defenses. The last of the lot is his best career victory to date, a convincing unanimous decision win over Miguel Cotto at New York City's Madison Square Garden in Dec. '12. Trout, who has family roots in Brooklyn, is the only fighter ever to claim a win over Cotto at MSG, where the Puerto Rican superstar has sold more tickets than any other boxer in the 21st century.

The feat was the last title fight hurrah for Trout, who dropped a 12-round decision to Canelo Alvarez in an April '13 clash in San Antonio, a bout that highlighted the ills of open scoring. The contest was seemingly competitive for eight rounds, only for WBC open scoring (Alvarez' title at the time, while Trout held the WBA belt) to reveal that the Mexican star was far enough ahead to where Trout needed a knockout in the final round rounds in order to prevail. A more convincing loss to Lara came later that December, having since scored four wins, with his last three coming by way of knockout.

Additional details of the show's eventual destination were not made available to BoxingScene.com as this goes to publish.

Jake Donovan is the managing editor of BoxingScene.com. Twitter: @JakeNDaBox